Electrical connector having a mercury amalgam coating on its inner surface



Oct. 13, 1953 A. G. ASAFF 2,655,641

ELECTRICAL CONNECTOR HAVING A MERCURY AMALGAM COATING ON ITS INNER SURFACE Filed on. 29, 1948 IN VEN TOR. 9. Asaff @MMM J Anna's Patented Oct. 13, 1953 ELECTRICAL CONNECTOR HAVING A MER- CURY AMALGAM COATING ON ITS INNER SURFACE Annis G. Asaff, Water-town, Mass., assignor to Aircraft-Marine Products Inc., Harrisburg, Pa.

Application October 29, 1948, Serial No. 57,249

Claims.

The present invention relates to an improvement in electrical connections.

One well known form of electrical connection comprises a terminal having a tongue portion, or the like, adapted to be engaged with a binding post or other terminal and a cylindrical ferrule or conductor engaging portion. In securing such a terminal to an insulated conductor of copper or other suitable wire, an end portion of the wire is stripped of its insulating covering and the ferrule portion of the terminal is slipped over the bareo. end of the wire and crimped thereon. The metal used in these connections is preferably such as to produce a coining effect, i. e., a flow or displacement of the metal under the crimping dies. The coined portions of the ferrule and the wire are thus pressed together to form in effect a solid or continuous mass, thus initially providing extended and intimate interface contact and correspondingly good electrical conductivity.

However, under certain conditions, corrosion, beginning at exposed portions of such a connection, tends to creep along the interfaces between the ferrule and the confined wire and, in cases where the conductor is of stranded copper wire, along the interfaces between the several wires as well. The effect of such corrosion is, of course, to increase substantially the contact resistance. These undesirable changes and their consequent disadvantages are avoided to some extent in the best types of soldered connections. However, soldered connections may deteriorate more rapidly in use than good crimped connections when both are exposed to the same deterioration producing conditions. Indeed, the solder, while presenting a satisfactory external appearance and producing initially low resistance, often serves to conceal defects. Moreover, the crimped, unsoldered connections can be more accurately evaluated as to condition by inspection and have other advantages, such as the shorter time required to make them and the fact that they are made without heating equipment and by simple tools requiring for their proper use very little training or skill.

One object of the present invention has been to provide an efiicient electrical connection, e. g., between a terminal and a conductor, binding post, or the like, which will not only have low initial electrical resistance but will also not develop increased resistance, even under adverse atmospheric or other conditions severe enough to produce deterioration or increased resistance in connections of the types heretofore known.

A further object of the invention has been to provide a terminal connection having the desirable properties of a soldered connection not only in respect to protection of contact areas against corrosoin but also in the stability of the union between the contacting parts; and which will also have the advantages in use and application of a crimped connection.

A further object has been to provide a connection between a conductor and a terminal which will not only resist corrosive forces and provide security of the bond but which will also afford a more extensive zone of conductivity than that presented by the areas of contact between the terminal and portions of the conductor actually engaged thereby.

Another object of the invention is to provide electrical elements, as terminals or the like, which will be better adapted than corresponding elements of known types for making either soldered or mechanically effected connections on the same element or between elements.

In accordance with teachings of this invention,

solid amalgam stable against evaporation is employed on a contact face of a connector terminal or other conductor, the surface of the amalgam being characterized by freedom from liquid film of mercury or amalgam and by the mercury being so effectively held by the amalgam that health hazards incident to exposed liquid mercury are avoided. According to this invention the amalgam on the coated electrical contact surface has sufficient mercury to give a spreading or diffusing effect with other metals brought into pressure contact therewith.

. In this specification and the accompanying drawings, I have shown and described a preferred embodiment of my invention and various modifications thereof, so far as it relates to the approved electrical connection device; and have described a preferred procedure and modification thereof according to my invention, so far as it relates to a method by which said connection device can be made. It is to be understood that said descriptions and drawings are not intended to be limiting of the invention, but on the contrary, are given for purposes of illustration in order that others skilled in the art may fully understand the invention and the principles thereof and the manner of applying it in practical use so that they may modify and adapt it in various forms or procedures, each as may be best suited to the conditions of a particular use.

In the accompanying drawings, in which exemplary embodiments for attaining the above objectives are set forth and in which like reference characters refer to like parts:

Figure 1 is a view in perspective of one form of electrical terminal to which the invention may be advantageously applied;

Figure 2, a central longitudinal section of the terminal of Figure 1;

Figure 3 is a view in side elevation of a modified form of the invention showing a terminal connected to a binding post;

Figure 4, a view in central longitudinal section of another type of terminal connector acmbodying my invention;

Figure 5, a view in perspectiveof an improved form of soldered connection embodying my Zinvention; and

Figure 6 is a view in cross-section illustrating a further modification of my invention embodied in an insulation penetrating type of connection. Referring to the drawings in greater detail, the conductor shown in Figure 1 comprisesan insulating cover I and a wire or'core 2 made up of strands of substantially pure high conductivity copper. The wire 2 has'secured at 'oneend a terminal, commonly of pure high conductivity copper, and comprised of a tongue portion 3, a ferrule 4, and a separately formed seamless sleeve H. Portions of said sleeve II embrace portions ID of said ferrule and are crimped or coined therewith when the ferrule is pressed into compressive contact with the bared end of the wire 2. Another portion of sleeve ll extends beyond the ferrule 4 to embrace an insulated portion of the conductor.

An embodiment of my invention, as appliedto the form of connection shown in Figure l, is illustrated more clearly in Figure 2, wherein the bared end of the multiple strand wire 2 is shown compressed within the crimped portions of ferrule 4. Inner surface portions of this ferrule and contiguous outer surface portions of said bared end of wire 2 are in effect merged through a-thin stratum of a mercury-tin or other suitable amalgam. 'Ihis amalgam stratum initiallyestablishes low resistance contact between the connected parts. Portions of the amalgam or mercury therein tend to flow or spread to adjacent surfaces of the conductor and the'terminal which are not in direct interengaging contact. It thus increases the effective'contact areas and'provides a highly conductive corrosive resistant bond-between the connected parts.

Effective electrical connections are produced according to my invention where suitable'metals,

or alloys thereof, which amalgamate with mercury are used to provide said amalgam stratum 5, especially those which have at least as great attraction or affinity for mercury as the copper or other metal of which the connected :parts are made, or with which they are coated.

Tests conducted under circumstances 'producing exaggerated adverse conditions'with respect to heat and/or salt sprays-have indicated that connections as above described, not-onl provide initial low resistancebutremain stable and maintain substantially unreduced electrical conductivity across the contact between the ferrule andthe conductor over extended periods of time; whereas connections similar'in every respect except for omission of said amalgam stratumi interposed in the area of pressure or contact between the ferrule and the conductor, have under identical conditions shown materially greater increases in electrical resistance due to corrosion at the contacts.

In one method of forming an electrical connection of the types and having the desirable characteristics above described, the metal surfaces to be connected are preferably cleaned or pickled and then treated to provide the amalgam stratum 5. For example, the amalgam forming said stratum 5 is deposited on saidconnectors or one of them, by applying a previously formed .amalgam of suitable consistency to said cleaned surfaces thereof, or electroplating thereon simultaneously or successively mercury and tin or .other .metal to be amalgamated. Or, the mercury component of the amalgam stratum is provided either before or after tin plating of the .perts by-dipping the ferrule, or end portions of the conductor wire, or both, into mercury; or ad- :vantageously, by :dipping the parts, or one of them, -.in a solution of a mercury salt. Amalgamation or formation of the amalgam stratum 5 is advantageously completed by plating or otherwise applying tinor other suitable metal on the mercurated part or parts, especially if the parts have not been previously tinned-or plated with other amalgamating metal.

The application'onto theface of a contact area of tin, or other suitable metal, either before, after or with mercuation is of practical advantage in holding the mercury at the-surface, without undue loss, especially-during long storage or under severe conditions and in arrestingexcessive diffusion of mercury into the-metal of one or more of the connected-parts. The'connector or terminal parts thus treated are rugged and durable and can be used effectively and safely either immediately or after extended periods of storage, handling, or transportation.

Where the parts shown in Figurel for example,

or suitable portions-of them, have been treated as above set forth, the wire-end that is to be fastened to a'terminal-is inserted within the ferrule '4 and compressed therein as by means of a crimping tool ina known manner, or as described in thepatent of 'S.N."Buchanan,No 2,379,567, dated July 3, 1945 to coin the ferrule and the enclosed wire into a very tight joint. The strength and the'electrical conductivity of said joint are 'enhancedby the presence of the amalgam stratum '5 formed either'between theferrule and the wire,

or interspersed among the'wires and between the ferrule'a-nd'the stranded wire, or both.

Although my inventionyso far as it involves the steps of method above set forth, is not limited to use in producing the above described connections, there is 'special'advantage in such use. Surface portions of various'metalsemployable as conductors orconnectors in'electrical practice develop a film of oxide when exposed to the air or other oxidizing conditions. This film on a'connector "or the like reduces the electrical conductivity thereof withanother connector Or'the like,'and, in addition,'impedes surface wetting'and welding or soldering of the connector surface-with other metals.

'With'my invention, asapplied to terminals for example, the mercury amalgam stratum 5 on the connected parts effectively seals or excludes air from the underlying metal surfaces. The cold working, as in crimping a ferrule or'terminal on a conductor, may possibly break the oxide film and thus allow mercury to effect close contact with or penetrate into the underlying or contiguous metal to give in effect a continuouslow resistance connection between the parts; or it may be that, under crimping'or otherpressure, mercury from the amalgam diffuses through '5 pores or holes in the oxide layer to provide an all metallic electrically conductive bond between the connected parts.

When solder is applied to the amalgamated or mercury treated surfaces of the wire ends and the terminal tongue 3, Figure 5, the solder, as 8, flows and \vets them easily, even without a flux and without their being heated other than by the heat derived from the molten solder itself.

In a modified procedure, the assembly of the wire or conductor with the ferrule crimped thereon as above described, both advantageously being of tinned electrical copper, is amalgamated, as by dipping into a solution of a suitable mercury salt, preferably containing a wetting agent to facilitate penetration of the solution into the crevices at the borders of the crimped ferrule. The mercury solution enters through the outer open end of the ferrule and creeps or spreads along portions of the ferrule and the compressed wires to form thereon or therebetween, an amalgam or mercury complex stratum which has the effect of protecting the underlying surfaces and maintaining and extending the areas of conductivity between the connected parts.

Mercuration can be effected conveniently with metallic mercury, or with solutions of ionizable mercury compounds, the anion of which forms a soluble salt with the metal on which the mercury is to be applied. Mercury salt solutions, especially a saturated aqueous solution of mercuric or mercurous nitrate in three per cent (3%) nitric acid, or a ten per cent (10%) solution of mercuric acetate in one per cent (1%) acetic acid, or a ten per cent (10%) solution of mercuric chloride in one per cent 1%) hydrochloric acid, have been efiectively employed. In any such case, the terminal, or the wire, or both, after cleaning to remove grease, oil, oxides, etc.. may be dipped into the solution. Where acid is used in the solution, it helps to remove the oxide layer, if any, and bring the mercury into direct metallic contact with the underlying metal, to that extent replacing a part or all of the cleaning treatment. Other agents for this purpose may be used as desired.

Advantages in the use of mercury salt solutions instead of metallic mercury or preformed mercury amalgam for the stated purpose are that said solutions in large part avoid health hazards and prejudices incident to use of metallic mercury, and that the amount of mercury applied may be more accurately controlled. Also, surface tension of such solutions can be readily controlled to give desired wetting of the surfaces under treatment. To this end one or more of the various known wetting agents can be added to the solution.

The proportion of mercury to tin in the mercury-tin amalgam referred to in the above described methods, or of mercury to another metal or alloy in a different but suitable amalgam, may vary widely according to circumstances. It has been observed that the initial electrical resistance between copper terminals secured on copper conductors, where the parts are connected through a stratum of mercury-tin amalgam, gradually declines as the proportion of mercury in said amalgam stratum is increased. However, since one object of my invention has been to provide a connection in which no substantial increase in electrical resistance across the contact occurs under conditions which would produce such increase in known forms of connections, it is desirable that the mercury-tin ratio of the amalgam be such as to produce optimum initial high conductivity with the minimum amount of mercury and to substantially maintain said high conductivity with minimum loss of mercury under commonly experienced conditions.

In general, the stability of an amalgam of a given mercury-tin ratio, other factors being constant, depends on temperature, the amalgam being less stable, i. e., losing more mercury, with increased temperature. I have found that a terminal-conductor connection with a forty-two per cent (42%) mercury fifty-eight per cent (58%) tin amalgam stratum has an acceptably low initial electrical resistance and is substantially stable at temperatures up to 185 C. and that a connection having a seventy-two per cent (72%) mercury and twenty-eight. per cent (28%) tin amalgam stratum has acceptably low resistance and is substantially stable up to 100 C. However, if otherwise necessary and practicable, the mercury content of the amalgam stratum may be increased with resulting increase in initial conductivity; but it will still remain stable at lower temperatures; or the mercury content may be decreased with decreasing initial conductivity, but with acceptable stability at higher temperatures. Although the amalgam itself is solid it may be in the liquidus-solidus range.

The presence of more mercury on the treated parts than is required to produce the beneficial results above noted not only involves needless expense, but may be otherwise undesirable. For example, where such parts are stored under conditions permitting evaporation, a possible health hazard may be created. Furthermore, when the amalgam stratum is used in contact with brass or certain other metals, an excess of mercury may, under some conditions, result in embrittlement or other deterioration of certain physical properties of such metals. These disadvantages are in large part avoided by limiting the mercury content of the amalgam stratum to approximately that percentage at which the amalgam remains stable or at which the mercury is held in alloy or solid amalgam under contemplated temperature conditions by the other metal or metals present at the same surface to which it is applied. Any liquid mercury on the surface of the treated parts should be removed, either by diffusion into the solid amalgam or by wiping off or otherwise, before the parts are distributed for use.

Whether the amalgam stratum is produced by applying mercury on tinned copper or by applying tin on mercurated copper, or by applying a previously formed amalgam of suitable consistency, the proportion of mercury in the mercu ry-tin amalgam stratum is, for practical purposes, and in View of the circumstances above noted, advantageously within the range of from five per cent (5%) up to seventy-five per cent I find that the preferred proportion of mercury in most cases is about fifty-five per cent (55%) by weight. For usual purposes and un der conditions where a mercury-tin ratio of approximately 55-45 is employed, the weight of the mercury content is advantageously approximately 4.5 milligrams per square centimeter of covered or treated area. where the amalgam stratum is 0.2 mils thick.

A further modification, as illustrated in Figure 3, provides a connection between a binding 0). 91199. 1, F1 connected *to'the tongue:-3 of any-desired form .of rterminal.

.A mercury-tin :amalgam is pro uc by :dipping said terminal :tongue in mmmn'y salt asolutionand 'tinning the flipp d par or otherwise, as above described. The zamalga coated tongue 3 pressed onto "the post 26 by the nut-l or equivalent pressure producing element. The pressure contacting surfaces -..of-said :post, said -nut, and said terminal fleeing :thus merged or, in effect, welded together, are -protected .by the mercury-tin amalgam stratum thereon. The connected parts therefore submtially maintain :the initial low resistance value across -,the :hond even under conditions which would ordinarily {result in increasing re- 'sistance.

:In Figure-4,1 :have shown one sform of switch, a common :pin type terminal plug or jack, -,designed for make .and break contact service, as :hyinsertion into and disconnection .from a co- -acting female :connector receptacle, not shown. In this case, applying a -mercury-tin;ama1gam stratum or equivalent treatment :to the surface ofssaid plug 'as a whole :assures L good ;low resistance connection thereof :to a conductor wire by crimping and/or soldering .an endportion of the :wire vin the ferrulelc forming part= of -Said;:plug. Good low-resistance connection ;'between the ,pin 3a of the plug and contact surfaces of the=fema1e connector receptacleis alsomade-bysaid stratum particularly where said receptacle surfaces are also :provided with an :amalgam stratum. .Such

desirably low resistance, w-hile possi,b ly .due in part to the :improved corrosionlresisting;prQDerties of the mercury treated contact surface or surfaces-may also be due in-part to-the relatively plastic quality or condition of the amalgam stratum near "the contact surface.

Ihave found-that while Imay make theamalgem with mercuryand materialsiother'than tin, tin appears to be instrumental in imparting permanent-plasticity-to .the stratum and hasthe efiect of'holding the mercuryagainst evaporation.

.Figure .6 illustrates a rsoldered -.connection wherein a terminal of electricalcopper, -.for example, :having a tongue portion 3 is secured to the end .of aconductor-in the-form of-a stranded copper wire, said terminal and said conductor end having.been:.-amalgam-treated as above described. Said parts thus treated are secured together byisolder z8-without thepse of flux and withoutapplying heat tothe parts other than that derived from the 'molten zsolder.

A furthei'imodification,shown in Figure =6, in- .cludes application of 'the inventionitoa connector of a type described and-.claimedina co-pending application of James '.C. Macy, Serial No. 679,630 .filedJune 27, :1946, now -Patent 2,557,126. Said connectors are convenientlyrsecnred to wireconductors of the stranded wire or solid wiretypes .or of the so-called tinsel -,or-s piral-on+a-;core type without stripping insulation therefrom, :by pressing-edge portions ofthe-connector through the insulation and .into contact -.with .portions of the underlying wire. For the purposes 'of the present invention, the connector Loixcollar -,9 has a stratum -of :mercury-tin, ror other suitable amalgam, applied or produced-as-above described. Edge portions of said amalgamated connector -9 are I forced inwardly through the insulating cover of the conductor, thus bringingamalgambearing surfaces .of said connectorinto contact .with the wirecore or portionsthereo'f. ,Un'derthese con- .ditions. mercury t nds t cr ep or flow {from :the collar. along surfaces'of theadjacent strands thus extending the area of amalgamatedsurfaee ;as well as theinumber of strands brought into effective electrical connection with the terminal through the amalgam layer. This results ,in favorable initial electrical conductivity and prolonged resistance to corrosion ,of the surfaces so joined. A connection of the .sort above .described is more satisfactory ;for some purposes .and more easily made than soldering or known :forms 10: crimped connections -in the ease .of ftinsel wire, because ofathefineness of the -wire strands thereof or-because said strands are:commanly interwoven or spun together with cotton .or other suitable :fiexible fibers.

Although "the use of my invention above described has demonstrated its effectiveness to produce the results stated, the exact causation .has not ,yet been certainly determined.

This application is a continuation-in-part ,of my prior application, Serial No. 551,141,, filed August .25, 1944.

:Lclaim:

1. .Ameleetrical terminal having a ,ferrule portion adapted to be crimped into engagement'with :the end 1.015 .a wire conductor, the ;ferrule portion ;of said connector being formed .of a metal and ,having ,an exposed solid urfacefilm consisting essentially :of a-stratum of amalgam, said amal- ,gam being :solidqand being further characterized by the presence of a metal having a hi her Iaflinity for -mercury than the metal of theconnector.

2. An electrical connector including a pair ,of solid :metalelements,:each having a solid contact surface for coaction with the contact surface -,of the other, ,one :,of said elements having on its .contact surface -.a stratum consisting substantiallysolelyvof a-solid amalgam-of-mercury with ametalhaving a higheramnity-formercury than the underlyingmetal of either of said-elements, said contact surfaces being pressed into contact.

3.14m electrical-connection comprising :a conductor, .a :terminal member in gripping contact with .a portion thereof, .and a stratum of an amalgam consisting of mercury and -tin interposed ,between said conductor and surface portions of the terminal in contact therewith .wherebyrelectricalconductivity in contact areas between-theterminaland the conductor is substantially maintained. said terminal and said wconductor.being made of-a metal having -a lesser ,aflinity for mercury than -;tin.

14. ,An electrical connector which comprises a ferrule-forming .portion adapted to embrace; and .engage a.wire,saidferrule-forming portion com- .ptising-asubstratemetaland a surface layer of amalgam on the wire-engaging face ,of-the ferrule-,formingportion, saidsurface amalgam compnsinga metal :havingahigher ailinity for mercury than ,the substrate ,metal, and .diffusible mercury in substantial proportion diffusiblefrom .sa1d.amalgam .to .another .metal when pressed thereon.

5.,An ,electrical .connector having a copper sleeve ,portion adapted .to embrace and engage a .copperconductor, said copper sleeve portion hailingat .least .its interior surface substantially .completelymoilered.with-ancxposed layer of an amalgam consisting of mercury and tin.

ANNIS ,G. .ASAFF.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Bobo Nov. 8, 1927 r Weder Sept. 28, 1937 o Weder Sept. 28, 1937 Goldstein Nov. 14, 1939 Conradi et a1 July 2, 1940 Xenis May 5, 1942 10 Number Number Name Date Hackbarth Nov. 24, 1942 Bahr Mar. 2, 1943 Buchanan July 3, 1945 Carlson et a1 Aug. 6, 1946 Johnson Nov. 2, 1948 FOREIGN PATENTS Country Date England of 1865 

